Visible light communication technology using visible light recognizable by human eyes to perform wireless communication has received attention. Light-emitting devices configured to emit visible light are found in various forms including lighting apparatuses installed in houses, in offices, or on roads, displays, electronic devices, traffic lights, and display apparatuses such as electronic bulletins everywhere in daily life. Only providing a communication function to apparatuses including such light-emitting devices can easily create a wireless communication environment.
In particular, in conventional wireless communication of mobile phones, wireless LANs, and the like, transmission power cannot be increased generally due to the influence of electromagnetic waves on human body. In contrast, in visible light communication, an electric power as high as several watts used for illumination can be utilized as it is for transmission. By taking advantage of such a feature, effective use of the visible light communication is expected in locations where wireless communication has not been available.
For example, the wireless communication using electromagnetic waves may not be used in hospitals, airplanes, and the like due to the influence of the electromagnetic waves on precision instruments. However, when visible light is used, the wireless communication can be used without influencing electronic devices. Moreover, light-emitting diodes (LEDs) which have become widely available for general illuminating apparatuses and display apparatuses can be turned on and off at a higher speed than conventional incandescent lamps, fluorescent lamps, etc. Thus, high-speed data transmission is possible by utilizing the LEDs. As described above, the visible light communication has features such as being ubiquitous, having high safety and high speed. Therefore, expectations for the visible light communication are growing to serve as a novel communication system.
As a visible light communication system, Japanese Unexamined Patent Publication No. 2003-318836 (hereinafter referred to as Patent Document 1), for example, shows a system including an illumination light transmitter configured to transmit a signal by using illumination light of a white LED and an illumination light receiver configured to receive the signal. Specifically, an illumination light transmitter includes a white LED made of a blue LED and a fluorescent material, an illumination light receiver includes a light receiving element and a blue filter configured to block light emitted from the fluorescent material and having a low response speed, and the illumination light transmitter and the illumination light receiver are used so that only direct light from the blue LED is used for optical communication. This can increase the speed of the communication.